In general, compressed air is supplied to or discharged from an air suspension which is mounted in a vehicle as a height controlling device from an onboard air compressor not only to suppress a change in the height of the vehicle (vehicle height) which occurs as the weight of a load, for example, changes but also to control the vehicle height appropriately so as to match it with the driver's preference or the like.
In addition, an onboard air compressor for supplying compressed air to an air suspension is such that a reciprocating compressor is driven by an electric motor so that air taken into the reciprocating compressor is compressed for supply to the air suspension.
In recent years, an improvement in response speed in controlling the vehicle height has been desired, and one of methods for improving the response speed, a method is adopted in which compressed air is accumulated in an air reservoir or tank. By adopting this method, it is possible to supply a required amount of compressed air to the air suspension from the air tank momentarily in controlling the vehicle height.
When the compressed air accumulated in the air tank is supplied to the air suspension, however, compressed air which is higher in pressure than that of compressed air that is used in the air suspension needs to be accumulated in the air tank. In conjunction with this, as such a reciprocating compressor, a reciprocating compressor is necessary which can compress compressed air to a high pressure.
A two-stage reciprocating compressor is said to be effective as the reciprocating compressor which can compress compressive air to the high pressure. This two-stage reciprocating compressor includes a casing which has a first cylinder and a second cylinder which are disposed so as to surround a crank chamber, an electric motor which is mounted on the casing and which has a rotating shaft, first and second pistons which are inserted in the first and second cylinders, respectively, so as to reciprocate therein, and first and second connecting rods which are attached to the first and second pistons, respectively, at ends thereof and which are situated in the crank chamber at the other ends thereof where a first bearing and a second bearing are provided, respectively. Additionally, the first and second connecting rods are attached to the rotating shaft of the electric motor via an eccentric member which is provided in inner circumferences of the first and second bearings (for example, refer to Japanese Unexamined Patent Publication No. 2007-205207).